The present invention relates to the general field of combustion chambers for turbomachines. It relates more particularly to the problem posed by assembling an annular combustion chamber in which the axial walls and the end wall of the chamber are made out of materials having coefficients of thermal expansion that are different.
In the field of aviation, it is becoming more and more widespread to use high-temperature composite materials of the ceramic matrix composite (CMC) type instead of metals when making various components of a turbomachine, and in particular its combustion chamber. The use of a combustion chamber that is made entirely out of metal is completely unsuitable from a thermal point of view because of the very high temperatures of the combustion gases. This reduces the lifetime of the combustion chamber.
However, composite materials are very expensive and present relatively low strength when faced with high levels of mechanical stress. Thus, use of such materials is usually limited to the axial walls of the combustion chamber, while the radial wall (i.e. the end wall of the chamber) that unites these axial walls at their upstream ends continues to be made more conventionally out of metal.
Unfortunately, metals and composite materials present coefficients of thermal expansion that are very different. This leads to problems in the systems for assembling the combustion chamber between the axial walls that are made of composite material and the chamber end wall that is made of metal. In particular, the use of conventional bolt systems is no longer possible from the point of view of the mechanical strength of the walls.
In order to remedy that drawback, publication EP 1 479 975 discloses using fastener tabs that are secured to the chamber end wall and via which it is secured to the axial walls. Although that solution is advantageous, it nevertheless presents numerous disadvantages. In particular, such an assembly system does not make it possible to provide expansion that is sufficiently free, while also providing effective damping of the vibration to which the chamber end wall is subjected in operation. As a result, the fastener tabs are subjected in operation to very high levels of bending stress that are particularly harmful to the mechanical strength of the assembly, and in particular to the strength of the composite.